The invention relates to an extruder head for orienting fibers in the sidewall of an elastomer-fiber composite hose or tubular conduit, but more particularly, the invention relates to an extruder head with a pin and die configuration which permits extruding hose at both large and small internal diameters (e.g., from about 21/2 inches down to about 1/4 inch) while orienting fibers in the hose sidewall for satisfactory burst characteristics.
Elastomeric hose may be formed with an extruder head that has a convergently tapered pin from head inlet to head outlet and a coaxial die that is also convergently tapered from head inlet to outlet. Together the pin and die define a conically convergent annular gap through which an elastomer is expelled to form a hose or conduit. Some pin and die configurations may also include a cylindrical extension of the pin and die to form what is known as a "land." An example of a conically tapered pin and die without a land appears in U.S. Pat. No. 4,044,799.
A divergently tapered pin and correspondingly coaxial divergent die with a land is known to desirably orient fibers of an elastomer-fiber composite stock generally longitudinally and circumferentially when the exit formed by the annular gap between the pin and die is two, and preferably at least three times greater than the extrusion head entry area formed by the annular gap between the pin and die. An example of a "divergent" pin and die arrangement for extruding elastomer-fiber composite tubing is disclosed by U.S. Pat. No. 4,056,591. A process for extrusion of hose through such dies is disclosed in U.S. Pat. No. 4,056,591. While such extrusion heads with a divergent pin and die arrangement are suitable for extruding elastomer-fiber composites to form a hose with oriented fibers for desirable burst characteristics, the size range of hose which can be produced with the head is particularly limited (e.g., internal diameters, I.D., between about 0.65 inches and about 1.0 inch). The size restrictions occur because of the area ratio limitations from inlet to exit required for selective fiber orientation. The restriction is particularly evident when the annular gap exit is at the preferred ratio of at least 3 times the annular gap inlet area. The pin diameter becomes so small at internal diameters below 0.65 inch that the pin will not either support itself or withstand the extruding pressures. For example, assuming a 0.15 wall gauge hose and an expansion area ratio from extrusion head inlet to extrusion head outlet of 3, the minimum prior art pin diameter at entry for a 0.625 inch I.D. would be 0.097 inches. For the same expansion ratio and wall gauge, a 0.375 I.D. hose would require a minimum pin die diameter of 0.025 inches; obviously, the pin could not support itself with such a minimum amount of material. When the hose internal diameter is reduced to 0.25 inches, which is a common size such as used for fuel line hoses, the pin diameter becomes negative and therefore impossible to make.
At the larger hose diameters, (e.g., 2.55 inch) the pin size may not have sufficient cross-section to withstand extruding pressures, (e.g., extruding pressures of 2800 psi).